design, construction, and performance of new generation open graded friction course (ogfc)

8/9/2019 Design, Construction, and Performance of New Generation Open Graded Friction Course (OGFC)

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DESIGN,CONSTRUCTION,ANDPERFORMANCEOFNEW-GENERATIONOPEN-GRADEDFRICTIONCOURSES

By

RajibB.Mallick

PrithviS.KandhalL.AllenCooley,Jr.DonaldE.Watson

ThispaperwaspublishedintheJournaloftheAssociationofAsphaltPavingTechnologists,AsphaltPavingTechnology,Volume69,2000

277TechnologyParkway Auburn,AL36830


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DESIGN,CONSTRUCTION,ANDPERFORMANCEOFNEW- GENERATIONOPEN-GRADEDFRICTIONCOURSES

By

RajibB.Mallick

AssistantProfessorWorcesterPolytechnicInstituteWorcester,Massachusetts

PrithviS.Kandhal

AssociateDirectorNationalCenterforAsphaltTechnology

AuburnUniversity,Alabama

L.AllenCooley,Jr.ResearchEngineer

NationalCenterforAsphaltTechnologyAuburnUniversity,Alabama

DonaldE.Watson

GeorgiaDepartmentofTransportationForestPark,Georgia

ThispaperwaspublishedintheJournaloftheAssociationofAsphaltPavingTechnologists,AsphaltPavingTechnology,

Volume69,2000


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DISCLAIMER

Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

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ABSTRACT

Open-gradedfrictioncourse(OGFC)hasbeenusedbyseveralstatedepartmentsof

transportation(DOT)since1950.WhilemanyDOTsreportgoodperformance,manyotherstatesstoppedusingOGFCduetounacceptableperformanceand/orlackofadequatedurability.Avastmajorityofthestatesreportinggoodexperienceusepolymermodifiedasphaltbindersandarelativelycoarseraggregategradationcomparedtotheotherstatesreportingunsatisfactoryperformance.Obviously,thereisaneedtodevelopanimprovedmixdesignproceduretohelpthehighwayagenciesinsuccessfuluseofOGFC.

TheprimaryobjectivesofthisstudyaretoevaluatetheperformanceofOGFCinthelaboratory

withdifferentgradationsandtypesofadditives,andrecommendarationalmixdesignprocedureforthenew-generationOGFCmixes.Additionally,theconstructionandperformanceofsixOGFCpavements(constructedpriortothisstudy)arediscussed.ThesemixesgenerallymeettherequirementsforgradationbandandCantabroabrasionrecommendedinthenewmixdesignsystem.

SeveralpolymersandfiberswereusedinOGFCmixes.Themixeswereevaluatedfordraindown,permeability,Cantabroabrasion,rutting,andmoisturesusceptibility.Atentativemixdesignsystemforthecoarsenew-generationOGFChasbeenrecommended.BasedupontheevaluationofsixOGFCfieldpavements,ithasalsobeenshownthatOGFCmixesmeetingthenewmixdesignrequirementsareconstructibleandhaveexhibitedgoodperformance.

KEYWORDS:open-gradedfrictioncourse,OGFC,mixdesign,polymermodifiedbinder,fiber,

draindown,abrasion,permeability,moisturesusceptibility

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Mallick,Kandhal,CooleyJr.,&Watson

DESIGN,CONSTRUCTION,ANDPERFORMANCEOFNEW-GENERATIONOPEN-

GRADEDFRICTIONCOURSES

RajibB.Mallick,PrithviS.Kandhal,L.AllenCooley,Jr.,andDonaldE.Watson

INTRODUCTIONOpen-gradedfrictioncourse(OGFC)hasbeenusedsince1950indifferentpartsoftheUnitedStatestoimprovethesurfacefrictionalresistanceofasphaltpavements.OGFCimproveswetweatherdrivingconditionsbyallowingthewatertodrainthroughitsporousstructureawayfromtheroadway.Theimprovedsurfacedrainagereduceshydroplaning,reducessplashandspraybehindvehicles,improveswetpavementfriction,improvessurfacereflectivity,andreducestrafficnoise.TheFederalHighwayAdministration(FHWA)developedamixdesignprocedureforOGFC(1)in1974,whichwasusedbyseveralstatedepartmentsoftransportation(DOTs).WhilemanyDOTsreportedgoodperformance,manyotherstatesstoppedusingOGFCdueto

unacceptableperformanceand/orlackofadequatedurability(2).However,significantimprovementshavebeenmadeduringthelastfewyearsinthegradationandbindertypeusedin

theOGFC.Recently,asurvey(3)ontheexperienceofstateswithOGFCwasconductedbytheNationalCenterforAsphaltTechnology(NCAT).AlthoughexperienceofstateswithOGFChasbeenvaried,halfofthestatessurveyedinthisstudyindicatedgoodexperiencewithOGFC.Morethan70percentofthestateswhichuseOGFCreportedservicelifeofeightormoreyears.About80percentofthestatesusingOGFChavestandardspecificationsfordesignandconstruction.Avastmajorityofstatesreportinggoodexperienceusepolymermodifiedasphaltbinders.Also,gradationsofaggregatesusedbythesestatestendtobesomewhatcoarsercomparedtogradationsusedearlierandgradationsusedbyotherstates.ItseemsthatgooddesignandconstructionpracticeisthekeytoimprovedperformanceofOGFCmixes.ThereisaneedtodevelopanimprovedmixdesignproceduretohelpthestatesinsuccessfuluseofOGFC.Awell-designedandwell-constructedOGFCshouldnothaveraveling/delaminationproblems

andshouldreasonablyretainitshighpermeabilityandmacrotexture.

Objective

TheprimaryobjectiveofthisstudywastoevaluatethelaboratoryperformanceofOGFCwithdifferentgradationsandtypesofadditives,andbaseduponthisworkrecommendarationalmixdesignsystemforanew-generationOGFC.Additionally,theconstructionandperformanceofsixOGFCpavements(constructedpriortothislaboratorystudy)arediscussed.ThesemixesgenerallymeettherequirementsforgradationbandandCantabroabrasionrecommendedinthenewmixdesignsystem.

SCOPEOFWORK

ThemajorperformanceproblemsassociatedwithOGFCcanbeclassifiedintotwocategories:ravelinginOGFCandstrippinginunderlyingasphaltcourses.ThemajorcausesofravelinginOGFCarebelievedtobeinadequateasphaltbinderfilmthickness,excessiveagingofbinder,andlossofasphalt-aggregateadhesionunderfreeze-thawconditions.WhenOGFCwaspromotedbytheFederalHighwayAdministration(FHWA)inthe1970s,manystateseitheradoptedFHWA'smixdesignmethod(1)orusedarecipemixcomposition.Sincepolymermodifiedasphaltbinderswerenotavailableatthattime,andnofiberswereused,designasphaltcontentsinOGFCmixeswerekeptrelativelylowbecauseofbinderdraindownproblemsduringstorageand/ortransportation.SomestatesalsoexperiencedsignificantlossinpermeabilityofOGFCafter2-3yearsbecauseofcloggingofvoidsbydeicingmaterialsorotherdebris.

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Thefollowingquestionswereraisedtodevelopatestplanforevaluatingdifferentgradationsand

additivesinthisstudy:1)WhatisagoodgradationforOGFCtoprovide

a)adequatepermeabilitytodrainwaterquicklyandmaintainareasonable

permeabilityduringservicelife?b)adequatestabilitythroughstone-on-stonecontacttominimizerutting?

2)Whatkindofadditive(s)isneededtoa)preventdraindownofbinderatbindercontentsneededtoprovidesufficient

binderfilmthickness?b)improveruttingresistanceanddecreasetemperaturesusceptibility?c)resistexcessiveaging?

Toanswerthesequestions,thestudywasdividedintotwomainparts.First,alaboratorystudy

wasconductedtoevaluatedifferentOGFCgradationsandtypesofadditives.Baseduponthislaboratorywork,anewOGFCmixdesignsystemwastoberecommended.Withinthenewdesignsystem,gradationbands,volumetricproperties,andperformancerelatedtestsweretobe

identified.ThesecondpartofthestudyentailedidentifyingOGFCpavementsectionsthatwouldcloselyresembleOGFCmixesresultingfromtherecommendedmixdesignsystemanddocumentconstructionandperformance.

LaboratoryStudy

AflowchartforthelaboratorystudytestplanisshowninFigure1.InthefirstphaseofthestudyblendswerepreparedwithgradationssimilartoandcoarserthantheFHWArecommended(1)gradationforOGFCmixes.Table1andFigure2givetheFHWAgradationandtheotherthreenewgradationsevaluatedinthisstudy.TheFHWAgradationhas40percentmaterialpassingthe4.75mmsieve,andthecoarsestoftheotherthreegradationshas15percentmaterialpassingthe4.75mmsieve.ThecoarsestgradationisverysimilartothegradationthatisbeingusedbymanystatesreportinggoodexperiencewithOGFCmixes(suchasGeorgia).Mixeswerepreparedfor

theseblendswithanunmodifiedPG64-22asphaltbinder.ThepropertiesofaggregateandasphaltbinderareshowninTables2and3,respectively.MixdesignswereconductedaccordingtoFHWAprocedures(1).Thesefourblendswereevaluatedforstone-on-stonecontactwithvoidsinthemineralaggregate(VMA)andvoidsinthecoarseaggregate(VCA)plots,andVCAdatafromdryroddedtestswithcoarseaggregatesfractiononly.TheVCAconceptisusedinthedesignofstonematrixasphalt(SMA)mixtures( 4).

SamplespreparedwithFHWAgradationandcoarsergradationsweretestedfordraindown

potential,permeability,abrasionresistance,agingpotential,andrutting.Thetestproceduresarediscussedlater.Allsampleswereinitiallycompactedwith100gyrationsofSuperpavegyratorycompactor,whichwereconsideredtobeequivalentto50blowsofMarshallhammerinSMAmixdesign.Theprimaryobjectiveofphase1wastoevaluatetherelativeimprovementsinmixcharacteristicswhentheFHWAgradationismadecoarserandcoarser.

Inthesecondphaseofthestudy,mixeswerepreparedwiththecoarsestgradation(gradation#3

inTable1)andsixdifferentbinders:PG64-22,PG64-22plusStyrene-Butadiene-StyreneorSBS(referredtohereinafterasPG64-22-SBS),PG76-22containingStyreneButadieneorSB(referredtoasPG76-22-SB),PG64-22pluscellulosefiber(referredtoasPG64-22-CF),PG76-22containingStyreneButadieneandslagwool(referredtoasPG76-22-SB-SW)andPG64-22plusslagwool(referredtoasPG64-22-SW).BothSBSandSBwereaddedtotheasphaltbinderat4percentbyweightofbinder.ThePG64-22and76-22(withSB)binderswerethebasebinders,towhichthedifferentadditiveswereadded.ThepropertiesofPG64-22and76-22(withSB)bindersareshowninTable3.Celluloseandmineralfiber(slagwool)wereaddedat0.37percentbyweightofthetotalmix.TheprimaryobjectiveofthesecondphasewastoevaluatetheperformanceofvariousadditivesintheOGFCmix.Basedondiscussionwithpersonnelfromthe

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Figure1.TestPlan3


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Table1.GradationsUsed

PercentPassingSieveSize Original Gradation New New New

FHWA Similarto Gradation#1Gradation#2 Gradation#3Gradation FHWAUsed

19mm --- 100 100 100 100

12.5mm 100 95 95 95 95

9.5mm 95-100 65 65 65 65

4.75mm 30-50 40 30 25 15

2.36mm 5-15 12 77 70.075mm 2-5

433 3

100

90

80

70

6050

40

30

20

10

0

0 0.0.20.0150.03075 .4 .6 0..680 1181.21. 1.4361.62. 1.8 4.752 2.2 2.4 2.69.52.8 312.53.2 3.4 3.6 193.8 4

SieveSize

FHWAgradation,40%passing4.75mmsieve 30%passing4.75mmsieve25%passing4.75mmsieve 15%passing4.75mmsieve

Figure2.GradationsUsedintheStudy

4

PercentPassin


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GeorgiaDepartmentofTransportation(GDOT),thesemixeswerepreparedwith6.5percent

asphaltbinder,andcompactedwith50gyrationstomatchairvoidcontentsofOGFCcoresamplesobtainedfromthefieldwheresimilargradationhadbeenused.Thesemixeswerealsotestedforthedifferentpropertiesmentionedearlier.Resistancetomoisturedamagewasalso

evaluatedinphase2.

Table2.PropertiesofAggregates

Aggregate

Granite

Size

Fine

Coarse

Property

BulkSpecificGravity

WaterAbsorption,percent

FineAggregateAngularity

BulkSpecificGravity

WaterAbsorption,percent

Value

2.712

0.63

49.5

2.688

0.58

Table3.PropertiesofPG64-22and76-22(withSB)AsphaltBinder

Asphalt HighTemperatureproperties LowTemperatureProperties Binder(PG) Temp

oeratureC

OriginalDSR,G*/Sin*

RTFOTDSR,G*/Sin*

TempoeratureC

RTFOT+PAV,DSR,

TempoeratureC

RTFOT+PAV

(kPa) (kPa) G*Sin* Creep m(Mpa) Stiffness, (slope)

S(MPa)

64-22 64 1.784 3.258 22 4426 -12 240 0.317

76-22 76 1.478 2.356 31 4450 -12 155 0.32(withSB)

FieldStudyTovalidatethepotentialforthenewmixdesignsystem,OGFCpavementswerefoundthatwouldcloselymeetrequirementsforthenewmixdesignsystem.SixOGFCpavementsectionswerelocatedonInterstate75southofAtlanta,Georgia.Thesesectionswereconstructedin1992andconsistofOGFCmixeswithdifferenttypes/combinationsofasphaltadditives.

ConstructionofthesesixpavementswasdocumentedinaGDOTreport(5).Additionally,

representativesofNCATperformedavisualdistresssurvey.Duringthesurvey,rutdepthsforeachsectionandthreecorespersectionwereobtained.Thecoreswereusedtomeasuredensityandlaboratorypermeability.

LABORATORYTESTPROCEDURES

Thefollowingtestprocedureswereusedinthelaboratorystudy.

VoidsinCoarseAggregate(VCA)

Similartostonematrixasphalt(SMA),OGFCmusthaveacoarseaggregate(retainedonNo.4.75mm)skeletonwithstone-on-stonecontacttominimizerutting(4).Theconditionofstone-

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on-stonecontactwithinanOGFCmixisdefinedasthepointatwhichthevoidsincoarse

aggregate(VCA)ofthecompactedOGFCmixtureislessthantheVCAofthecoarseaggregatealoneinthedryroddedtest(AASHTOT19).TheVCAofthecoarseaggregateonlyfraction(VCADRC)isdeterminedbycompactingthestonewiththedry-roddedtechniqueaccordingtoAASHTOT19.Whenthedry-roddeddensityofthestonefractionhasbeendetermined,theVCA

DRCcanbecalculatedusingthefollowingequation:

where,GCA(s

(w

=bulkspecificgravityofthecoarseaggregate(AASHTOT85)=unitweightofthecoarseaggregatefractioninthedry-roddedcondition

(kg/m3)(AASHTOT19)

=unitweightofwater(998kg/m3

)DraindownCharacteristicsTheNCATdraindowntestmethod(4)wasused.Asampleoflooseasphaltmixturetobetestedispreparedinthelaboratoryorobtainedfromfieldproduction.Thesampleisplacedinawirebasketwhichispositionedonaplateorothersuitablecontainerofknownmass.Thesample,basket,andplateorcontainerareplacedinaforceddraftovenforonehouratapre-selectedtemperature.Attheendofonehour,thebasketcontainingthesampleisremovedfromtheovenalongwiththeplateorcontainerandthemassoftheplateorcontainerisdetermined.Theamountofdraindownisthencalculated.

Thistestmethodcanbeusedtodeterminewhethertheamountofdraindownmeasuredforagivenasphaltmixtureiswithinacceptablelevels.Thetestprovidesanevaluationofthedraindownpotentialofanasphaltmixtureduringmixturedesignand/orduringfieldproduction.Thistestisprimarilyusedformixtureswithhighcoarseaggregatecontentsuchasporousasphalt(OGFC)andSMA.Amaximumdraindownof0.3percentbyweightoftotalmixisrecommendedforSMAandisalsoconsideredapplicabletoOGFC.

Permeability

TheFloridaDOTfalling-headlaboratorypermeabilitytestwasused.Thistestusesafallingheadconcepttodeterminepermeability(6).

ResistancetoAbrasion

TheresistanceofcompactedOGFCspecimenstoabrasionlosswasanalyzedbymeansoftheCantabrotest(7).ThisisanabrasionandimpacttestcarriedoutintheLosAngelesAbrasionmachine(ASTMMethodC131).

Inthistest,anOGFCspecimencompactedwith50blowsoneachsideisused.Themassofthe

specimenisdeterminedtothenearest0.1gram,andisrecordedasP1.ThetestspecimenisthenplacedintheLosAngelesRattlerwithoutthechargeofsteelballs.Theoperatingtemperatureisusually25C.Themachineisoperatedfor300revolutionsataspeedof30to33rpm.Thetestspecimenisthenremovedanditsmassdeterminedtothenearest0.1gram(P

2).Thepercentage

abrasionloss(P)iscalculatedaccordingtothefollowingformula:

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Therecommendedmaximumpermittedabrasionlossvalueforfreshlycompactedspecimensis20percent(5).However,someEuropeancountriesspecifyamaximumvalueof25percent.

Resistancetoabrasionusuallyimproveswithanincreaseinbindercontent.However,this

resistanceisalsorelatedtotherheologicalpropertiesofthebinder.Foragivengradationandbindercontent,mixescontainingunmodifiedbindersgenerallyhavelessresistancetoabrasionthanmixescontainingpolymer-modifiedbinders.

Aging

BothunagedandagedcompactedOGFCweresubjectedtoCantabroabrasiontesttoevaluatetheeffectofacceleratedlaboratoryagingonresistancetoabrasion.Becauseofveryhighairvoid

contentstheasphaltbinderinOGFCispronetohardeningatafasterratethandense-gradedhotmixasphalt(HMA),whichmayresultinreductionofcohesiveandadhesivestrengthleadingtoraveling.Therefore,themixdesignshouldbesubjectedtoanacceleratedagingtest(7).

AgingwasaccomplishedbyplacingfiveMarshallspecimenscompactedwith50blowsina

forceddraftovensetat60Cfor168hours(7days).Thespecimensarethencooledto25Candstoredfor4hourspriortoCantabroabrasiontest.Theaverageoftheabrasionlossesobtainedon5agedspecimensshouldnotexceed30percent,whilenoindividualresultshouldexceed50percent.

FreezeandThawTestforResistancetoMoistureDamage

RavelingoftheOGFCmaytakeplaceduetostrippinginthemix,especiallyfromfreezeand

thawcyclesinnortherntierstateswithcoldclimates.ModifiedLottmantest(AASHTOT283)wasusedinthisstudy.Insteadofusingonefreeze/thawcycleusedfordense-gradedHMA,5cycleswereusedforOGFC.SincetheairvoidcontentishigherintheOGFCcomparedtodense-gradedHMA,moresevereconditioningwasdeemednecessarytoevaluatethestrippingpotential.

Rutting

ThepotentialforruttingofOGFCwasevaluatedwiththeAsphaltPavementAnalyzer(APA)whichisamodifiedversionofGeorgialoadedwheeltester.CylindricalOGFCspecimenswereloadedat64C(bothdryandunderwater)for8000cyclesandrutdepthmeasured.

DEVELOPMENTOFMIXDESIGNPROCEDURE

Asummaryofdataandanalysesusedtodevelopthemixdesignsystemarepresentedinthefollowingsections.

PhaseOne

TwoblendswithcoarseaggregateonlywerepreparedaccordingtotheAASHTOT19proceduretodeterminethedryroddedvoidsincoarseaggregate(VCADRC).Next,threeblendswerepreparedforeachgradationwith15%,25%,30%and40%passing4.75mmsieve.Asmentionedearlier,the40%passing4.75mmsieverepresentedFHWAgradationandtheremainingthreegradationswereallcoarserthantheFHWAgradation(Figure2,Table1).Since,ingeneral,theNCATsurveyindicatedgoodperformanceofmixeswithgradationscoarserthan

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theFHWAgradation(3),itwasdecidednottouseanygradationfinerthantheFHWA

gradation.MixeswerepreparedwithPG64-22asphaltbinderandcompactedwith100gyrationsoftheSuperpavegyratorycompactor(SGC).TheasphaltcontentsweredeterminedbytheFHWAmethod(1).TheFHWAmethodconsistsofthefollowingsteps:(1)determinationof

surfacecapacityofaggregatefractionretainedon4.75mmsievebyoilabsorptionmethod,and(2)determinationofasphaltcontentfromanempiricalformulawiththesurfaceconstant(obtainedinstep1).Thefollowingformulaisused:Table4givesthemixdesigndatausingtheFHWAprocedure.Unfortunately,theoptimumasphaltcontentisbasedontheoilabsorptionofthematerialretainedon4.75mmsieveonly.Therefore,theoptimumasphaltcontentsareverysimilarforallfourgradations,whichisnotlogical.Obviously,theFHWAformulawasdevelopedforonegradationband.

Table4.FHWAMixDesignData(PhaseOne)

Gradation(%passing4.75mmsieve)

15

25

30

40

PercentOilRetained(POR)

1.890

1.839

1.808

1.724

SurfaceConstant,Kc

0.856

0.836

0.823

0.789

AsphaltContent,percent

5.55

5.51

5.48

5.42

Theaverageairvoidsorvoidsintotalmix(VTM),voidsinmineralaggregate(VMA),voidsin

coarseaggregate(VCA),andvoidsfilledwithasphalt(VFA)dataforthefourdifferentmixesareshowninTable5.TheVCADRCisalsoshowninTable5.PlotsofVTM,VMA,andVCAareshowninFigures3and4.Althoughthereisadifferenceofonly0.13%inasphaltcontentbetweenthemixeswithfourgradations,thereisasignificantrangeinvoids(VTM,VMAandVCA).TheVTMandVMAgenerallydecreasewithanincreaseinpercentpassing4.75mmsieve.Hence,thecoarserthemix,thehigheristheVTMandVMA.ThedryroddedcoarseaggregateVCA(VCA

DRC)fallsbetweenthecompactedmixVCAvaluesforgradationswith

15%and25%passingthe4.75mmsieve.Thisindicatesthatstone-on-stonecontactbeginsatsomepointbetween25%and15%(approximatelyat22%)passingthe4.75mmsieve.

Table5.SummaryofMixVolumetricProperties

CompactedOGFCMixGradation(%passing4.75mmsieve)

AsphaltContent

TMD*VTM,%

VMA,%

VCA,%

VFA,%

15 5.55 2.47515.1 26.3 37.3 42.6

25 5.51 2.51214.3 24.5 43.3 41.7

30 5.48 2.51113.6 24.0 46.6 43.3

40 5.42 2.48712.5 23.9 54.1 47.3*TMD=TheoreticalmaximumdensityDryroddedVCA=41.7%.

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20

19

18

17

16

15

14

13

1211

10

0 5 10 15 20 25 30 35 40 45PercentPassing4.75mmSieve

Figure3.PercentPassing4.75mmSievevs.VoidsinTotalMix

Note:SamplesCompactedWith100GyrationsofSGC

55

VMA VCA50

45

40

35

30

2520

0 5 10 15 20 25 30 35 40 45

PercentPassing4.75mmSieve

Figure4.PercentPassing4.75mmSievevs.VMAandVCANote:Dry-RoddedVCA=41.7%

9

VoidsinTotal(MixVTM,%

)

Voids

%


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Also,theVMAcurvestartstocurlupward(VMAincreases)atabout30%passing4.75mm

sieve.ThereducedslopeinVMAindicatesstone-on-stonecontactisbeginningtobelost,andfurtherincreasesintheamountofthefineaggregatedonotbringtheaggregatesanycloser.HighVTMassociatedwiththecoarsergradationwillalsofacilitatebetterdrainageofwater.A

preliminary,crudetestcarriedoutbyholdingcompactedOGFCspecimensunderwatertapindicatedalmostfreeflowofwaterthroughthemixwith15%passingthe4.75mmsieve,moderateflowthroughmixwith25%passing4.75mmsieve,andverypoorornoflowthroughmixeswith30%and40%passingthe4.75mmsieve.

Draindown

Inhotmixasphalt,thecoarserthegradation,thegreateristhepotentialofdraindownofasphaltbinderduringstorageand/ortransportation.Draindowncausesdeficientbinderinpartofthemix(resultinginraveling)andexcessivebinderintheotherpartofthemixcausingbleedinglossofpermeability,andpotentialforflushingandrutting.DraindowntestswereconductedonuncompactedOGFCmixes(withPG64-22binder)at160Cand175CaccordingtotheNCAT

draindowntestmethod.TheSchellenbergdrainagetestusedinEuropeisconductedat175C(7).TheresultsofNCATdraindowntestareshowninTable6.Themaximumpermissibledraindownis0.3%.Asexpected,themixwith15%passing4.75mmsieveshowedthemaximumdraindown.Themixwith25%passing4.75mmsieveshowedadraindownoflessthan0.3%at175C.However,whentestedwithPG76-22binder,themixwith15percentpassingthe4.75mmsieve,showedsignificantlylessdraindown.Itshouldbenotedthatthetemperaturesusedfordraindowntestsinthisstudyaresignificantlyhigherthantypicalproductiontemperatures.OGFCmixescontainingpolymermodifiedbinderssuchasSBorSBSarecommonlyproducedat150C.Itisrecommendedtoconductthedraindowntestattheproposedmixingtemperature.Nonetheless,thetestdatainTable6givestherelativedraindownpotentialofdifferentmixes.

Table6.SummaryofDraindownTestResults

Draindown(%)Gradation(percentpassing

4.75mmsieve)

15

25

30

40

PG64-22

0.45

0.10

0.11

0.12

160C

PG76-22

0.05

PG64-22

1.27

0.25

0.24

0.19

175C

PG76-22

0.30

AbrasionTest

TheCantabroabrasiontestwasconductedonmixeswithdifferentpercentagesofmaterialpassingthe4.75mmsieve.First,theunagedsamplesweretested.Next,sampleswereagedandtestedforabrasionloss.TheresultsareshowninTable7.Thedatashowthatunderbothagedandunagedconditionstheabrasionlossincreasesasthemixismadecoarser,themixwith15%passing4.75mmsieveshowsthehighestabrasionloss.Although,themixwith15%passing4.75mmsievesatisfiestheCantabroabrasioncriteria(7)of20%maximumforunagedspecimensand30%maximumforagedspecimens,thelosscanbereducedfurtherbyusingamodifiedbinderandincreasingtheasphaltcontentbyuseoffibers.Thiswasinvestigatedinthesecondphaseofthestudyreportedlater.

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Table7.SummaryofAbrasionTestResults

Gradation(percentpassing4.75mmsieve)

1525

30

40

Loss,%(Unaged)

14.712.1

11.7

8.1

Loss,%(Aged)

29.319.6

17.2

15.5

Differenceduetoaging(%)

14.67.5

5.5

7.4

PermeabilityThepermeabilityofmixeswithdifferentpercentagesofmaterialpassingthe4.75mmsieveweretestedwithafallingheadpermeameter.ThecoefficientsofpermeabilityobtainedforthedifferentmixesareshowninTable8.Asexpected,themixeswithlowerpercentageofmaterial

passingthe4.75mmsieveshowhigherpermeability.Thereisasignificantincreaseinpermeabilitybetweenthemixwith30percentpassingthe4.75mmsieveandthemixwith15percentpassingthe4.75mmsieve.Forcomparison,coarsegradedSuperpavemixeshavebeenfoundtohavepermeabilityintherangeof1.5mperdayto8.8mperdaywithvoidsrangingfrom6.4to8.8percent(testedwiththeFloridaPermeabilityTestMethod)(6).

Table8.SummaryofPermeabilityData


15

25

30

40

Rutting

Permeability(coefficient,m/day)

117

8828

21

Ruttestswereconductedonthefourmixesatdesignasphaltcontents.TheAsphaltPavementAnalyzer(APA)wasusedtorutthemixesunderawheelloadof445N(100lb),andahosepressureof690kPa(100psi).Themixesweretestedat64C,sincethePGgradeoftheasphaltwasPG64-22.Table9showstheresultsofruttests.Therutdepthsat8,000cyclesdonotshowawiderange,nordoesitshowanyparticulartrendwithpercentpassingthe4.75mmsieve.However,alloftherutdepthsareverysmall,lessthan5mm,andareconsideredacceptable.

Table9.SummaryofRutData


15

25

30

40

RutDepthat8000cycles,mm

4.05

3.83

4.29

3.41

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PhaseTwo

Inthenextphaseofthelaboratorystudy,mixeswerepreparedwith15percentpassingthe4.75mmsieveand6.5percentasphaltcontentusingsixdifferentbinder/additivecombinations.Test

samplesforthesixmixeswerecompactedwiththeSGC,usingthenumberofgyrationsrequiredtoachieveairvoidsclosertothosefoundinthefieldatthetimeofconstruction(about18percent).

Astudywascarriedouttodeterminetherequirednumberofgyrations.Threesamplesofeach

mixwerecompactedwith100gyrationsoftheSGCand50blowsofMarshallhammer.Theairvoidsatdifferentgyrationswerecomparedtoairvoidsgenerallyfoundinthefieldandtheairvoidsofthesamplecompactedwith50blowsMarshall(Figure5).Itwasdeterminedthatabout50gyrationswiththeSGCand50blowswiththeMarshallhammerproduceabout18percentairvoidsgenerallyfoundinthefield.Themixeswerepreparedwithsixdifferenttypesofbinderasdescribedearlier:PG64-22,PG64-22-SBS,PG76-22-SB,PG64-22-CF,PG76-22-SB-SWandPG64-22-SW.Thesamplesweretestedforvolumetricproperties,draindown,aging,rutting,and

moisturesusceptibility.ThevolumetricpropertiesareshowninTable10.Resultsfromothertestsarediscussedinthefollowingparagraphs.

242220

181614

121086420

VoidsinSpecimenCompactedwith50BlowsofMarshallHammer

0 20 40 60 80 100 120

NumberGyrationsinSGC

Figure5.Gyrationsvs.VTMplot.

12

VoidsinTotalMix

VTM

%


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Table10.VolumetricPropertiesofMixesWithDifferentBinders(AverageValues)

Binder BulkSp. TMD VTM VMA VCAGr.

PG64-22 2.044 2.441 16.3 29.0 37.3PG64-22withcellulose 2.043 2.441 16.3 29.0 37.3

PG64-22withslagwool 2.071 2.441 15.2 28.1 37.3

PG64-22withSBS 2.026 2.441 17.0 29.6 37.3

PG76-22-SB 2.002 2.441 18.0 30.5 37.3

PG76-22withslagwool 2.046 2.441 16.2 28.9 37.3

DraindownTheaveragedraindownvaluesat157C(315F)areshowninTable11.Thetesttemperatures

werereducedinPhase2torepresentproductiontemperaturesgenerallyusedinthefield.ResultsfromamultiplecomparisontestarealsoshowninTable11.Theseresultsindicatewhetherthereisanysignificantdifferencebetweenthedifferentmeansandifthereis,providestherankingofthedifferentmixesbasedonthemeans.Table11indicatesthatthedraindownvaluesaresignificantlyhigherforallmixeswiththePG64-22andthePG76-22-SBandalsodonotmeetthecriteriaof0.3percentmaximum.ItseemsthatSBS,slagwool,andcellulosearemoreeffectiveinreducingthedraindownathighertemperatures.

Table11.ResultsofDraindownTestsFromMixesWithDifferentBinders

Draindownat157C(315F)

DuncanGrouping Mean(%) AsphaltBinder

A 1.3585 PG64-22

A 1.1845 PG76-22-SB

B 0.5405 PG64-22withSBS

B 0.1245 PG76-22-SBwithslagwool

B 0.0510 PG64-22withslagwool

B 0.0040 PG64-22withcellulose

AgingTestSamplesofmixespreparedwithdifferentbindersweretestedwiththeCantabroabrasiontesttodeterminetheeffectofaging.Allofthesampleswereagedat160Cfor168hours(7days).

Table12showsthetestvaluesandtheresultsofmultiplecomparisontest.TheresultsshowthatthemixeswithunmodifiedPG64-22binderhavethehighestabrasionloss,andthemixeswithPG76-22-SWhavethelowestabrasionloss,withtheothermixeshavingvaluesinbetween.Ingeneral,mixeswithPG64-22plusSBSandthePG76-22-SBbindersshowlessabrasionthanmixeswiththeotherbinders.Althoughallmixesmeetthemaximumlosscriteriaof30percent,itappearsthatthecombineduseofpolymermodifiedbinderandfiberwillminimizetheabrasionlossfromagingandthusincreasethedurabilityoftheOGFC.

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Table12.AbrasionLoss(AgedSamples)forMixesWithDifferentTypesofBinder


A 26.2 PG64-22

B A 19.3 PG64-22withslagwool

B A 18.8 PG64-22withcellulose

B C 15.7 PG76-22-SB

B C 13.0 PG64-22withSBS

C 9.0 PG76-22withslagwool

RuttingTestRuttingtestswereconductedonsamplesofmixeswithdifferentbinderswiththeAPAusingidenticalproceduresasphase1.Table13showsthemeansandtheresultsofmultiple

comparisontest.TheresultsshowthatingeneralmixeswithPG76-22-SBbindershowlessruttingcomparedtomixeswithPG64-22binder.OfthemixeswithdifferentPG64-22binders,themixeswiththeunmodifiedbindershowedthehighestamountofrutting,whiletheonewithSBSshowedtheleastamountofrutting.ThelowestrutdepthwasobtainedincaseofSBmodifiedPG76-22withslagwool.Again,thecombineduseofapolymer-modifiedbinderandfiberresultedinthelowestrutdepth.

Table13.RutDepthforMixesWithDifferentTypesofBinder


A 6.28 PG64-22

B A 5.24 PG64-22withcellulose

B C 5.00 PG64-22withslagwool

B C 4.70 PG64-22withSBSD C 3.81 PG76-22-SB

D 2.70 PG76-22withslagwool

MoistureSusceptibilityTestMoisturesusceptibilityofmixeswasevaluatedbyconductingtensilestrengthtestonconditioned(5freeze/thawcycles)andunconditionedcompactedsamples(airvoids71percent)ofmixeswithdifferentbinders.Thistestwasincludedinphase2toevaluatetheeffectofbindertypeandfibersonthemoisturesusceptibilityofOGFCmixes.Table14showstheaveragevaluesoftensilestrengthratiosobtainedforthedifferentmixes.TheresultsshowthatmixeswithPG64-22-SBSshowthehighestTSR(100percent),whereasthemixeswithunmodifiedPG64-22showthelowestTSR(below70percent).Ingeneral,allthemixes,exceptthosewithunmodifiedPG64-22andPG64-22-SWshowTSRvaluesgreaterthan80percent.Itappearsthatbothpolymer-modifiedbinderandfibershouldbeusedespeciallyinthenortherntierstatesoftheU.S.,whichexperiencecoldclimatesandfreeze/thawcycles.

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Table14.TSRValuesforMixesWithDifferentBinders

AsphaltBinder Mean(%)

PG64-22withSBS

PG76-22withslagwoolPG64-22withcellulosefiber

PG76-22-SB

PG64-22withslagwool

PG64-22

SUMMARYOFLABORATORYSTUDYThefollowingobservationscanbeobtainedfromthelaboratorystudy:

10098

91877562

1.Agradationwithnomorethanabout20percentpassingthe4.75mmsieveis

requiredtoachievestone-on-stonecontactconditionandprovideadequatepermeabilityinOGFCmixes.2.Mixeswith15percentaggregatespassingthe4.75mmsievearesusceptibleto

significantdraindownofthebinder.Therefore,itisnecessarytoprovideasuitablestabilizersuchasfiberinthemixtopreventexcessivedraindown.

3.AbrasionlossofOGFCmixesresultingfromagingcanbereducedsignificantlywiththeadditionofmodifiers.Inthisstudy,allofthemodifiedbindershadsignificantlylowerabrasionlossthantheunmodifiedbinder.Theuseofbothpolymer-modifiedbinderandfibercanminimizetheabrasionlossandthusincreasethedurabilityofOGFC.

4.Forthebindersusedinthisstudy,rutdepthsasmeasuredwiththeAPAdidnotvaryoverawiderange.However,withintherangeofrutvaluesobtained,themixeswithmodifiedbindershadsignificantlylessruttingthanmixeswithunmodifiedbinders.A

higherPGbindergradeseemstohaveagreatereffectinreducingruttingthanalowerPGbindergrade.Apolymer-modifiedasphaltwithfibergavetheleastamountofrutting.

5.Moisturesusceptibility,asmeasuredbyTSRvalues,islowerformixeswithmodifiedbindersthanmixeswithunmodifiedbinders.Allofthemodifiersexceptslagwool(withPG64-22)producedmixeswhichhadTSRvaluesinexcessof80percent.Again,bothpolymer-modifiedbinderandfibershouldbemosteffectiveespeciallyincoldclimateswithfreeze/thawcycles.

TentativeOGFCMixDesignProcedure

Thefollowingtentativemixdesignsystemisrecommendedforthenew-generationOGFCmixesonthebasisofthelaboratorystudy,observationofin-placeperformanceofOGFCmixesinGeorgia,andexperienceinEurope.Thesystemcanberefinedfurtherasmoreexperienceisgainedinthefuture.

Step1.MaterialsSelection

ThefirststepinthemixdesignprocessistoselectmaterialssuitableforOGFC.MaterialsneededforOGFCincludeaggregates,asphaltbinders,andadditives.Additivesincludeasphaltbindermodifiers,suchaspolymersandfibers.

GuidanceforsuitableaggregatescanbetakenfromrecommendationsforSMA(4).Thebinder

selectionshouldbebasedonfactorssuchasenvironment,traffic,andexpectedfunctionalperformanceofOGFC.Highstiffnessbinders,suchasPG76-xx,madewithpolymersare

15


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recommended(5)forhotclimatesorcoldclimateswithfreeze-thawcycles,mediumtohigh

volumetrafficconditions,andmixeswithhighairvoidcontents(inexcessof22percent).Theadditionoffiberisalsodesirableundersuchconditionsandalsohavebeenshowntosignificantlyreducedraindown.Forlowtomediumvolumetrafficconditions,eitherpolymer

modifiedbindersorfibersmaybesufficient.

Step2.SelectionofDesignGradation

BaseduponthislaboratorystudyandrecentexperiencesinGeorgia,thefollowingmastergradationbandisrecommended.

Sieve

19mm

12.5mm

9.5mm

4.75mm

2.36mm

0.075

mm

PercentPassing

100

85-10055-

7510-25

5-10

2-4

Selectionofthedesigngradationshouldentailblendingselectedaggregatestockpilestoproducethreetrialblends.Itissuggestedthatthethreetrialgradationsfallalongthecoarseandfinelimitsofthegradationrangealongwithonefallinginthemiddle.Foreachtrialgradation,determinethedry-roddedvoidsincoarseaggregateofthecoarseaggregatefraction(VCADRC).Coarseaggregateisdefinedastheaggregatefractionretainedonthe4.75mmsieve.

Foreachtrialgradation,compactspecimensatbetween6.0and6.5percentasphaltbinderusing50gyrationsofaSuperpavegyratorycompactor.Iffibersareaselectedmaterial,theyshouldbeincludedinthesetrialmixes.Determinethevoidsincoarseaggregate(VCA)foreachcompactedmix.IftheVCAofthecompactedmixisequaltoorlessthantheVCADRC,stone-on-stonecontactexists.Toselectthedesigngradation,chooseatrialgradationthathasstone-on-stonecontactcombinedwithhighvoidsintotalmix.

Step3.DetermineOptimumAsphaltContent

Usingtheselecteddesigngradation,prepareOGFCmixesatthreebindercontentsinincrementsof0.5percent.Conductdraindowntestonloosemixatatemperature15Chigherthananticipatedproductiontemperature.Compactmixusing50gyrationsofaSuperpavegyratory

compactoranddetermineairvoidcontents.ConducttheCantabroabrasiontestonunagedandaged(7days@60C)samples.RuttingtestswiththeAsphaltPavementAnalyzerandlaboratorypermeabilitytestingareoptional.Insufficientdatawasaccumulatedinthisstudytorecommendacriticalrutdepth.However,laboratorypermeabilityvaluesgreaterthan100m/dayarerecommended.Theasphaltcontentthatmeetsthefollowingcriteriaisselectedasoptimumasphaltcontent.

1.AirVoids.Aminimumof18percentisacceptable,althoughhighervaluesaremoredesirable.ThehighertheairvoidsarethemorepermeabletheOGFC.

2.AbrasionLossonUnagedSpecimens.TheabrasionlossfromtheCantabrotestshouldnotexceed20percent.

3.AbrasionLossonAgedSpecimens.TheabrasionlossfromtheCantabrotestshouldnotexceed30percent.

4.Draindown.Themaximumpermissibledraindownshouldnotexceed0.3percentby

totalmixturemass.

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Ifnoneofthebindercontentstestedmeetallfourcriteria,remedialactionwillbenecessary.Air

voidswithinOGFCarecontrolledbythebindercontent.Ifairvoidsaretoolow,theasphaltbindercontentshouldbereduced.Iftheabrasionlossonunagedspecimensisgreaterthan20percent,moreasphaltbinderisneeded.Abrasionlossvaluesofagedspecimensinexcessof30

percentcanberemediedbyeitherincreasingthebindercontentorchangingthetypeofbinderadditive.Ifdraindownvaluesareinexcessof0.3percent,theamountofbinderand/ortypeofbinderadditivecanbeadjusted.Fiberstabilizersaretypicallyincorporatedintothemixatarateof0.2to0.5%ofthetotalmix.

Step4.EvaluateMixforMoistureSusceptibility

ThemixdesignedwithStep1through3shouldbeevaluatedformoisturesusceptibilityusingthemodifiedLottmanmethod(AASHTOT283)withfivefreeze/thawcyclesinlieuofonecycle.Theretainedtensilestrength(TSR)shouldbeatleast80percent.

CONSTRUCTIONOFTESTSECTIONS

In1992,theGDOTinitiatedafieldstudytoevaluateOGFCmixes(5).TheprimaryobjectiveofthisstudywastocompareGDOTconventionalOGFCswithcoarserOGFCsmodifiedwithdifferentbinderadditivecombinations.Thiswasaccomplishedbyconstructingsixtestsectionsusingacoarsergradationwithsixcombinationsofpolymer/additiveonI-75southofAtlanta,Georgia.

ThesixtestsectionswerecharacterizedasacoarseOGFC(D),coarseOGFCwith16percent

crumbrubber(D16R),coarseOGFCwithcellulosefibers(DC),coarseOGFCwithmineralfibers(DM),coarseOGFCwithSBpolymer(DP),andcoarseOGFCwithSBpolymerandcellulosefibers(DCP).Mixdesignsforeachofthesemixeswasconductedusingthe"MethodofDeterminingOptimumAsphaltContentforOpen-GradedBituminousPavingMixtures,"whichisastandardprocedureforGDOT(GDT-114).

Job-mix-formula(JMF)dataforeachofthesixmixesarepresentedinTable15.Thistable

showsthatallsixOGFCmixeshadidenticalgradationsandonlydifferedbyrespectiveasphaltcontents.Ofinterest,theJMFgradationfallswithinthegradationbandrecommendedinthenewmixdesignsystem(Figure6).

Table15.LaboratoryTestResultsfortheSixOGFCMixes(6)

Test D D16R DM DC DP DCP

Percentpassing19.0mm 100 100 100 100 100 100



Percentpassing4.75mm 18 18 18 18 18 18Percentpassing2.36mm 8 8 8 8 8 8


PercentAsphaltBinderofTotalMix

%AC 6.0 6.6 6.3 6.4 6.2 6.4

OtherTestData

Cantabro(%Wear) 13.5 8.6 5.7 5.8 8.6 8.2

Drainage(%Loss) 0.37 0.05 0.06 0.06 0.34 0.04

17


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Figure6.GradationofOGFCFieldTestSections

TestsconductedinadditiontothemixdesignincludedtheCantabroabrasionandSchellenbergDrainagetests.ResultsoftheCantabroabrasiontestindicatedthatallsixoftheOGFCmixeswouldmeettherequirementof20percentlossmaximumrecommendedintheproposedmixdesignsystem.Infact,forthefivemixescontainingbinderadditives,abrasionlossvalueswerealllessthan9percent.ThoughtheSchellenbergDrainagetestisnotidenticaltothe

NCATdraindowntest(4),fourofthesixmixesmettypicalSchellenbergdrainagerequirementsof0.3percentbytotalbindermass.Ofthetwomixesnotmeetingthe0.3percentdraindown,oneusednopolymers/additives(D)andtheotherusedjustapolymer(DP).

Productionofthemixesinthefieldwasaccomplishedwithadouble-barreldrumplant.The

plantwasmodifiedslightlyinordertoincorporatethecrumbrubberandfibersintothemixingprocess.Duringproduction,trucksampleswereobtainedtodetermineasphaltcontent,gradation,airvoids,andCantabroabrasionlossvalues.Table16presentstheresultsofthistesting.

BasedonTable16,fiveoftheproducedmixeswerefinerthantheJMFgradationonthe4.75

mmsieve.Onlyonegradation(DM)didnotmeettherecommendedgradationbandwithinthe

newmixdesignprocedure.However,thismixonlyvariedfromthebandby1.2percentonthe9.5mmsieve.Asphaltcontentsrangedfrom5.9to6.4percent.Airvoidcontentsoflabcompactedsamplesusing25blowsperfaceofaMarshallhammerrangedfrom10.9to14.1percentandarelowerthanwouldbeanticipatedontheroadway.Cantabroabrasionlossvaluesrangedfrom7.0to15.7percentandarealllowerthanthesuggested20percentmaximumcriteria.

18


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Table16.LaboratoryTestResultsforFieldProducedOGFCMixes( 6)

SampleType JMF D DM DC DCP DP D16R

SieveSize,mm TotalPercentAggregatePassingbyWeight

19.0 100 100 100 100 100 100 100

12.5 99 98.3 98.9 96.7 97.0 99.1 96.3

9.5 75 70.0 76.2 64.0 68.6 69.9 60.3

4.75 18 21.0 23.9 19.0 19.1 23.1 15.7

2.36 8 8.7 9.0 7.7 7.8 8.4 7.4

0.075 2 3.6 3.1 2.8 2.4 3.1 2.6

MiscellaneousTestData

AsphaltContent Extracted 5.85 6.22 6.16 6.14 6.25 6.41

TMD --- 2.484 2.445 2.429 2.424 2.476 2.451

VTM --- 12.2 11.4 11.5 10.9 14.1 12.0

Cantabro(%Wear) --- 10.3 8.1 14.7 7.0 15.9 7.6

Inadditiontotestingtrucksamples,coreswereobtainedfromeachofthesixtestsections.Testingofthesesamplesincludedasphaltcontentsandgradationsbyextractionandairvoidcalculations.Anadditionaltestconductedwasthein-placepermeabilityofeachsection.ResultsofthistestingarepresentedinTable17.

Table17.LaboratoryTestResultsforRoadwayCoreSamplesfromOGFCTestSections

SampleNo. JMF D DM DC DCP DP D16R

SieveSize,mm TotalPercentAggregatePassingbyWeight19.0 100 100 100 100 100 100 100

12.5 99 99.3 98.6 99.2 97.6 99.3 99.2

9.5 75 77.3 77.2 75.5 73.1 76.5 76.7

4.75 18 28.1 28.3 28.0 26.9 27.8 28.0

2.36 8 13.1 13.6 13.7 13.0 13.1 13.1

0.075 2 3.8 4.1 3.5 3.9 3.8 3.4

MiscellaneousTestData

AsphaltContent Extracted 5.51 5.87 6.18 5.27 5.85 5.69

VTM --- 17.8 17.2 16.4 16.0 17.6 18.1

Permeability --- 46 82 71 71 84 67(m/day)

OfnoteinTable17arethein-placeairvoidcontentsofthecompactedmixes.Airvoidcontentsrangedfrom16.0to18.1percentwhichrelatewelltothedataaccumulatedinthelaboratorypartofthisstudy(Table10).Thesevaluesalsoseemtovalidatetheselectionof18percentairvoidsminimumduringthenewmixdesignsystemasmixesmeetingthegradationrequirementscanbeconstructedtohave18percentairvoids.Permeabilityvaluesobtainedfromthesixtestsectionsrangedfrom46to84m/dayandappeartocorrespondreasonablywellwithpermeabilitydatafromthelaboratoryworkinthisstudy(Table8).

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DataobtainedfromthisGDOTfieldstudyindicatethatOGFCmixesmeetingthegradation

requirementsoftherecommendedmixdesignprocedurecanbeproducedsuccessfullyinthefield.Also,becauseofthetestingproceduresusedbyGDOTintheirfieldstudy,itisbelievedthatthesixmixeswouldbesimilartoOGFCmixesdesignedusingthenewmixdesign

procedure.Therefore,theperformanceofthesemixesinthefieldshouldprovidevaluableinformationonhowmixesdesignedwiththenewprocedurewouldperform.

PERFORMANCEOFTESTSECTIONS

During1998(sixyearsafterconstruction),representativesofNCATperformedavisualdistresssurveyonthesixOGFCtestsections(8).Thesurveyconsistedofevaluatingeachsectionforsurfacetexture,rutting,cracking,andraveling.Duringthecourseofthesurvey,coreswereobtainedfromeachsectionandusedtodeterminethelaboratorypermeability.AlsoreportedinthissectionaretheresultsoffrictiontestingconductedbytheGDOT3.5yearsafterconstruction(5).

VisualDistressSurvey

SurfaceTexture

Allsixtestsectionshadexperiencedsomecoarseaggregatepopout.TheD16RsectionappearedtohavethemostwhiletheDC,DM,andDPsectionsallhadaverylowamount.Anothersurfacetextureitemwastheexistenceofsmallfatspotsonthepavementsurface.Eachofthesixsectionshadthesefatspots.However,nonewerelargerthanapproximately15cmdiameter.TheDandDCPappearedtohavethemostbutwerenotdeemedsignificant.

Rutting

Rutdepthmeasurementsweremadeforeachsectionusingastringline.Rutdepthsrangedfrom0.0mmfortheDPsectionto4.1mmfortheDCsection.Noneofthesectionswerecharacterizedashavingsignificantamountsofrutting.

Cracking

TheprimaryformofcrackingonallsixsectionswasreflectivefromaPortlandcementconcretepavementunderlyingeachsection.Table18presentsdescriptionsandpercentagesofreflectivecracksencountered.Percentagesweredeterminedbycountingthenumberoftransversecracksvisibleatthepavementsurface.

Table18.SeverityandPercentageofTransverseReflectiveCracks

Section

D

D16R

DMDC

DP

DCP

Description

Lowtomediumseverity

Lowtohighseverity

LowseverityLowseverity

Lowtomediumseverity

Lowtomediumseverity

%CracksShowing

75

87

5545

61

65

Table18showsthatfiveofthesixsectionshadlowtomediumseverityreflectivecracking.ThetwoOGFCmixescontainingonlyfibers(DMandDC)hadtheleastamount(andseverity)ofcrackingwhiletheD16Rsectionhadthehighestamountandseveritycracking.Reflectivelongitudinalcrackswerealsoobservedonfivesections.OnlytheDandD16Rsectionshadwhatcouldbecharacterizedasmediumseveritylongitudinalcracking.

20


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Besidesreflectivecracking,onlytheD16Rsectionshowedanyothertypeofcracking.

Secondarycrackingaroundsomereflectivecrackshadoccurred.

Raveling

Allsixsectionsshowedsomesignsofraveling.However,allravelingwasminimalexcepttheD16Rsectionwhichshowedsomemediumseverityravelingnexttosomecracks.

PermeabilityTestingofCores

Three150mmcoreswereobtainedfromeachofthesixsections.Table19presentstheaveragelaboratorypermeabilityvaluesfromeachsectionaswellasaveragein-placeairvoidcontents.Statistically,nosignificantdifferencesexistbetweenthepermeabilityvalues;however,theDCandDCPsectionsdidhavethehighestaveragepermeabilityat74and70m/day,respectively.In-placeairvoidcontentsrangedfrom15to19percent.Bulkspecificgravitymeasurementsweredeterminedbyvolumetricmeasurements.Itisinterestingthatthisrangeofairvoidcontentscorrespondwellwiththeroadwaycoreairvoidcontents(atthetimeofconstruction)presented

inTable17.Again,thisappearstoprovidevaliditytotheselectionof18percentairvoidsminimuminthenewmixdesignsystem.ThiscriteriaappearstoberelatedtoairvoidcontentsatbothconstructionandduringthelifeofanOGFCpavement.Additionally,itappearsthatthemixdesignprocedureusedbyGDOTinthisexperimentresultedinOGFCmixeswithstone-on-stonecontacteventhoughitwasnotspecificallytested.

Table19.AveragePermeabilityandIn-PlaceAirVoidContentsfortheSixTestSections

Section

D

D16R

DM

DCDP

DCP

FrictionTesting

Avg.Permeabilitym/day

25

38

28

7416

70

Avg.In-PlaceAirVoids,%

16.7

15.8

19.9

16.213.9

19.2

FrictiontestingwasconductedbyGDOT3.5yearsafterconstructionaccordingtoASTME274procedures(5).Resultsofthistestingindicatedthatfrictionvaluesforthesixsectionsrangedfrom49to51.Thesevaluesweredeemedsatisfactory(5).

CONCLUSIONS

ResultsofthisstudyshowedthatacoarsergradationforOGFCmixesprovidesabetterperformingOGFCpavement.Gradationsnear15%passingthe4.75mmsieveperformedmuchbetterthanfinergradationsinthelaboratory.Modifiers,whetherpolymerand/orfibers,werealsoshowntoenhancetheperformanceofOGFCmixes.Usingthisknowledge,anewmixdesignsystemforOGFCmixeswasrecommended.

ConstructionandperformancedataforsixOGFCpavementsthatwouldcloselyresemblemixes

resultingfromthenewmixdesignsystemwerealsodiscussed.Basedupontheinformationobtainedfromboththelaboratoryandfieldwork,itisconcludedthatthenew-generationOGFCwillprovideabetterperformingmixture.

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REFERENCES

1.

2.3.

4.

5.

6.

7.

8.

Smith,R.W.,J.M.Rice,andS.RSpelman.DesignofOpen-GradedAsphaltFrictionCourses.ReportFHWA-RD-74-2,FederalHighwayAdministration,January1974.

Smith,H.A.PerformanceCharacteristicsofOpen-GradedFrictionCourses.NCHRPSynthesisofHighwayPractice180,TRB,1992.Kandhal,P.S.,andR.B.Mallick.Open-GradedFrictionCourse:StateofthePractice.TransportationResearchCircularNumberE-C005,TRB,December1998.Brown,E.R.,andL.A.Cooley.DesigningStoneMatrixAsphaltMixturesforRut-ResistantPavement.NCHRPReport425,TRB,1999.Santha,Lanka.ComparisonofStandardOpen-GradedFrictionCourseswithModifiedOpen-GradedFrictionCourses.GeorgiaDepartmentofTransportationResearchProjectNo.9110,FinalReport,April1997.FloridaDepartmentofTransportation."FloridaMethodofTestforMeasurementofWaterPermeabilityofCompactedAsphaltPavingMixtures."FM5-565,March1999.PorousAsphalt.Manual17,SabitaLtd,Roggebaai,SouthAfrica,November1995.

Cooley,Jr.,L.A.andE.R.Brown."EvaluationofOGFCPavementsContainingCelluloseFibers."NationalCenterforAsphaltTechnology.PreparedforInterfibeCorporation.April1999.

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